1. Field of the Invention
The present invention relates to a transmitting apparatus and, more particularly, to a transmitting apparatus in which information of another channel is inserted into information of one channel in a transmitting system for compressing information by a prediction coding and a non-prediction coding and transmitting the compressed information.
2. Related Background Art
A digital video tape recorder (VTR) is known as an image recording apparatus for digitally compressing a moving image and recording it onto a recording medium such as a magnetic tape or the like. There are a fixed length coding compression method and a variable length coding compression method as compression methods. As compared with the fixed length coding compression method, in the variable length coding compression method, although a high compression ratio of about 1/10 to 1/20 can be accomplished without largely deteriorating a picture quality, there is a drawback such that a compression data amount per picture plane (frame or field) is not uniform and it is difficult to perform editing (joint recording or the like), retrieval, and special reproduction (random access, fast forward reproduction, reverse reproduction, etc.).
An MPEG (Moving Picture Coding Expert Group) method uses an intra-frame (field) coding and a prediction coding which uses a future and/or past frame (or field) as a reference picture plane and periodically arranges the intra-frame coded picture plane (hereinafter, called an I frame) and, on the other hand, sets the picture plane in the I frame to a prediction coded picture plane. According to such a recording method, the compression data of an inter-frame prediction coding picture plane in the reverse direction or both directions is recorded after the compression data of the prediction reference picture plane on the recording medium.
According to such a recording method, for instance, a limitation occurs at the joint position of the image, for instance, in the insertion recording (joint recording). For example, even if the operator tries to join another picture plane just after the inter-frame prediction coding picture plane in the reverse direction or both directions, the image data of the picture plane which is necessary to decode such an inter-frame prediction coding image in the reverse direction or both directions needs to be preserved on the recording medium. On the other hand, a prediction relation between the old picture plane to be inserted and the new picture plane to be inserted becomes discontinuous in the joint portion, so that a reproduction picture plane becomes disorder.
Such a problem is not limited to only the VTR as mentioned above but a similar problem also occurs in case of inserting data of another channel to a predetermined insertion point of data of one channel.